A variety of metal-containing compositions (i.e., pastes, inks, tapes, films, etc.) are useful in forming electronic circuits or devices. These metal-containing compositions are used to produce electrically conductive conduits within the electronic circuits or devices. Generally, electronic devices or circuits comprise two or more layers of electrically conductive conduits or paths. Various techniques may be employed in order to electrically connect one conductive layer to another. One common technique is to form a via or opening through the insulative layer disposed between the conductive layers which are to be electrically connected. These vias or openings are then filled with a conductive paste (via fill paste). The via fill paste serves to provide an electrical bridge or connection between the conductive layers.
Because of its high electrical conductivity, and relatively low cost as compared to metals such as gold, silver is generally a preferred material for use in forming a conductive layer. However, as to exposed or surface applications, gold is many times preferred over silver. More particularly, silver has a propensity to migrate under conditions of high humidity. As a consequence, gold is many times the preferred material for forming a conductive surface layer in an electronic circuit or device.
Accordingly, if possible, it would be desirable when producing some multilayer electronic circuits or devices to utilize buried conductive layers made of silver and exposed layers made of gold. Unfortunately, however, electrically connecting a gold layer to a silver layer can present a problem. More particularly, the markedly different diffusion rates of gold and silver in each other and in other precious metals can produce a buildup of Kirkendahl voids at one or both of the conductor via interfaces resulting in an open circuit. This is why many electronic circuits or devices, such as circuits or devices produced using low temperature cofired tape, are made completely with silver (e.g., buried silver layers, silver via fills, and surface silver) or completely with gold.